JPH045889A - Printed wiring board - Google Patents

Abstract

PURPOSE:To prevent the increase of conductor thickness due to plating, and to improve the accuracy of the formation of circuits and the printing accuracy of a solder resist by previously forming a viscous non-plating substance layer on the surface of a metallic foil before the plating treatment of the inwall section of a through-hole. CONSTITUTION:Viscous non-plating layers 4 are disposed on the surfaces of the metallic foils 2 of a metal-clad laminated board 3 composed of a multilayer-board base material layer 1 and the metallic foils 2 as outermost surfaces. Layers consisting of a substance, on which electroless plating does not adhere, and capable of being simply removed after the plating treatment of the inwall section of a through-hole are used as the layers 4 at that time. The through-hole 5 is formed at the specified position of the board 3, and an electroless plating layer 6 and an electroless plating layer 7 are formed. Joining corner sections 8 are exposed by removing the layers 4, and plating treatment is executed, thus acquiring a printed wiring board 10, on which thin plating layers 9 are shaped, then forming circuits 11 having patterns required. The thickness of the layers 9 is brought to half or less of conventional devices, thus preventing the increase of conductor thickness, then improving the accuracy of the formation of circuits and the accuracy of the printing, etc., of a solder resist.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a printed wiring board. More specifically, the present invention relates to an improved printed wiring board that can prevent increase in conductor thickness due to plating treatment and improve circuit formation accuracy and solder resist printing accuracy.

(Prior art) In recent years, with the increasing demand for finer circuits for printed wiring boards, which are widely used in electrical and electronic equipment, communication equipment, computing equipment, etc., advanced circuit formation methods have been developed. There is a strong need for further improvement.

Regarding circuit formation on such printed wiring boards, it is known that one of the factors that determines the accuracy is the problem of increase in conductor thickness during through-hole plating of metal-clad laminates.

Conventionally, as a substrate for this printed wiring board, as shown in FIG. A through hole (1) is formed by processing a metal-clad laminate (2) in which a metal foil (B) is placed on the outermost surface of a multilayer board base material layer in which an inner circuit is embedded inside the material layer (A). A plated layer (e) is formed on the inner wall surface of the through hole (1) by electroless plating and electrolytic plating, and then a predetermined pattern of circuits (forces) is formed.

Various efforts have been made to improve the accuracy of drilling and plating.

(Problem to be Solved by the Invention) However, in the conventional printed wiring board manufacturing method, as can be seen from the process diagram in FIG.
(a) Since the metal surface conductor part consisting of through-hole holes becomes thicker due to the plating treatment after processing, it is difficult to set the width and undercut of the circuit formed in the etching process to a specified value. As the printed circuit becomes thicker, the problem of ink bleeding and blurring during the solder resist coating process cannot be avoided.

Therefore, this invention eliminates the drawbacks of through-hole drilling in the conventional manufacturing of printed wiring boards as described above due to the plating process after processing, prevents increase in conductor thickness due to plating, and improves circuit formation accuracy and solder resist. It is an object of the present invention to provide an improved printed wiring board that can improve printing accuracy and a method for manufacturing the same.

(Means for Solving the Problems) The present invention solves the above problems by providing a viscous non-plated layer on the metal foil surface layer of a metal-clad laminate, and plating the holes after processing to form a hole on the inner wall of the Sulpore. To provide a printed wiring board characterized in that a plated layer is formed on a portion, and a thinner plated layer is formed by removing a viscous non-plated layer.

(Function) In this invention, since a viscous non-plating substance layer is formed on the surface of the metal foil in advance before plating the inner wall of the through-hole, this plating process also prevents the plating from adhering to the metal foil conductor. Therefore, its thickness does not increase. In addition, after plating the inner wall, this non-plated layer is removed and a thin plating layer is formed in order to improve the continuity reliability of a part of the through-hole corner. Since the thickness of the plating layer deposited is 172 mm or less, the accuracy of circuit formation by subsequent etching and solder resist coating is significantly improved compared to the conventional case.

(Example) Hereinafter, a printed wiring board of the present invention will be explained along with the drawings.

FIG. 1 of the attached drawings shows the main part of the manufacturing process of the printed wiring board of the present invention.

(a) First, for example, a base material layer made by laminating a predetermined number of resin-impregnated glass base materials, resin films, etc., or a multilayer board base material layer (1) further incorporating an inner layer circuit, and a metal foil on the outermost surface ( A viscous non-plated layer (4) is provided on the surface of the metal foil (2) of the metal-clad laminate (3) consisting of (2) and (3).

There is no particular limitation on the structure of the metal-clad laminate (3) at this time, and it is formed by impregnating a base material such as a glass sheet, glass mat, or paper with a resin such as unsaturated polyester, epoxy, phenol, or polyimide. A predetermined number of sheets of prepreg or these resins are heated and pressed to form copper,
An appropriate material may be used, such as one in which a metal foil such as aluminum or stainless steel is disposed on the outermost layer.

The non-plated layer (4) provided on the metal foil (2) on the outermost surface shall be made of a material to which electroless plating does not adhere, and which can be easily removed after the plating treatment of the inner wall of the through-hole hole. Use as appropriate. Examples of this non-plated layer (4) include viscous substances such as wax and oligomers. These substances may form the non-plated layer (4) in a viscous adhesive state, semi-hardened state or hardened state. In addition, this non-plated layer (
4) can be applied and disposed using a roll, a doctor blade, or other appropriate means.

There is no particular limit to its thickness. It can fulfill its role in a very thin state.

(b) Next, through-hole drilling is performed at predetermined positions of the metal-clad laminate (3) on which the non-plated layer (4) is disposed, to form through-holes (5). A through hole (5) of a predetermined size is formed by means such as drilling or punching.

(c) The through holes (5) are first subjected to electroless plating to form an electroless plating layer (6), and further electrolytic plating is applied as needed to a predetermined thickness to form an electrolytic plating layer (6). 7).

At this time, since the non-plated layer (4) is provided on the surface metal foil (2), the plated layers (6) and (7) are not attached to the surface at all due to the presence of this non-plated layer (4). do not.

The plating treatment conditions can also be similar to those of a normal method.

(d) After plating, remove the non-plated layer (4) on the surface. Since this is formed using a material that can be easily applied and removed as the non-plated layer (4), it can be removed by simple means such as wiping or polishing.

When wax is used, it can be almost completely removed by wiping.

Note that cleaning may be performed if necessary.

By removing this non-plated layer (4), the through holes (5
) and the surface metal foil (2) (8) are sharply exposed.

(e) Therefore, in order to improve the conduction reliability of this corner part (8), plating is performed to form a thin plating layer (9).

- For boat fishing, it is sufficient that the thickness of this thin plating layer (9) is less than the conventional thickness of 172 mm. Since the plating layers (6) and (7) are already formed on the inner wall of the through hole (5),
A very thin layer is sufficient.

<f) The through-hole plating printed wiring board (10) thus formed is etched with a desired pattern of circuits (
11) can be formed.

In this circuit forming step, the suppression of the conductor thickness achieved by the above steps <a) to (e) improves the accuracy of circuit formation and the accuracy of solder resist ink printing. There is no ink bleeding or blurring when printing with resist ink.

For example, in accordance with step 1 above, through-hole drilling is performed using wax as the non-plated layer (4) from a copper-clad laminate, and the inner wall of the hole is plated, and the thickness is increased by plating the silver foil conductor layer. The precision of solder resist printing, circuit formation, and solder resist printing could be significantly improved compared to conventional methods.

(Effects of the Invention) As explained in detail above, the printed wiring board of the present invention suppresses the increase in conductor thickness caused by plating, and improves the accuracy of circuit formation by etching, etc., and solder resist printing, etc., compared to conventional methods. can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a main part of the manufacturing process of a printed wiring board according to the present invention. FIG. 2 is a process sectional view showing a conventional process. 1... Base material layer 2... Metal foil 3... Metal clad laminate 4... Non-plated layer 5... Through hole 6... Electroless plating layer 7... Electrolytic plating Layer 8...Corner part 9...Thin plating layer 10...Printed wiring board 11...Circuit

Claims (1)

[Claims] (1) A viscous non-plated layer is provided on the metal foil surface layer of the metal-clad laminate, and after drilling, a plating treatment is performed to form a plating layer on the inner wall of the through-hole, and the viscous non-plated layer is removed to create an even thinner plated layer. A printed wiring board characterized by forming.